Construction and design method

ABSTRACT

A retaining wall for supporting and stabilizing cut or fill areas of excavation. The wall is constructed by applying the concrete pneumatically. This method consists of temporarily installing a backing board while the vertical wall is pneumatically constructed. The footing and vertical call can be constructed monolithically utilizing this method. This method of construction yields a high strength wall with very few construction steps, has a high efficiency of the use of materials. The flexibility in the design and advantage with regards to accessibility along with a few number of workers are also a large benefit.

Construction and Design Methods

Footings

The footing can be sprayed in pneumatically (FIG. 1) (1). The horizontalrebar is required for lateral strength in the footing (2). The cut inthe soil for temporary access and for the footing requirements, shouldbe stable (3). The base of the footing (4) before concrete is shot orpoured in and should be stable and have a minimum specified friction andsoil bearing capacity per the final design specifications. The heel (5),which is the portion of the footing that will be under the bulk of theback fill (12), will hold the wall from overturning, sliding orsubsiding. The toe (6) will also aide in preventing the retaining wallto overturn or subside.

Vertical Wall

The vertical portion of the retaining wall will also be pneumaticallysprayed concrete (shotcrete, gunnite) (FIG. 1) (7). This verticalelement can be applied or sprayed at the same time as the footing andthereby create a monolithically constructed retaining wall. The verticalrebar (8) will be hooked and supported by using both the horizontalrebar (2) in the proposed footing (5) and the horizontal rebar in thevertical retaining wall (7). This horizontal rebar (9) rebar is used totemporarily stabilize the vertical rebar until the pneumatically appliedconcrete (shotcrete) can be applied (19). The horizontal bars in boththe footing (2) and the vertical portion of the retaining wall (9) areneeded not only for the rigidity of the rebar wall until the pneumaticconcrete is applied, but it is also required for the overall horizontalstrength that both members (footing and vertical wall) require.

Backing Board

The temporary backing board (FIG. 2) (13) is then attached to thevertical rebar (9) using wires or tiebacks (14). The backing board orpeg board (13) can be made of any flat material as long as it is tiedapproximately 2 inches or more away from the vertical rebar (8) toprevent rust and or corrosion in the future. The backing board is mostlikely to be ¼ inch peg board which is light weight and has holesdrilled approximately 1″ to 2″ on center in both directions(horizontally and vertically). This peg board or backing board can beremoved when the concrete has been set or it can be left in place. Ifthe backing board/peg board is left in place, the back fill material orearth can be place against the board. Leaving the board in place is anoption, and has no structural affect on the retaining wall.

Pneumatically Applied Concrete

The pneumatically applied concrete will be shot from the gun (16) fromthe opposite side of the peg board (13). The concrete will be applied inlayers (15) so that there will not be too much force or weight againstthe backing board (13) at any given time. The application of theconcrete in this fashion (pneumatically) is what allows this method ofretaining wall construction to be carried out. This method is unlikecast in place concrete walls that require heavy materials to carry outthe construction of the forms. It is a simple, inexpensive, andexpeditious technique of constructing a concrete retaining wall. Thepneumatically sprayed concrete (FIG. 2) (19) is delivered by a pump (18)through a hose (17) out of a gun (16).

Hydrostatic Relief

Hydrostatic pressure should be relieved behind the retaining wall in thesame fashion as the conventional block retaining wall See FIG. 3). Thiscan be achieved by placing 2″ to 3″ diameter PVC (20) every 6 foot oncenter just above the outside finished grade. The back side of the wallor filled portion (12) should have a continuous horizontal rock pocket(19) with river rock or equal consisting of 1″ to 2″ rounded river rock.In addition to this a filter fabric (21) can be installed if desired.This filter fabric will keep the soil fines from entering the voids ofthe river rock (weep rock) (19) and thereby allowing the hydrostaticpressure to be relieved more effectively. Other methods of relievinghydrostatic pressure can also be used: such as a 4″ perforated drainpipe (see FIG. 4) (22) running parallel to the footing with river rock(weep rock and filter fabric) and eventually day lighting or gravityflowing out to a lower elevation (23).

Elimination of Stair Stepping

The footings when excavated do not have to be vertically stair stepped(FIG. 5.)(25). Because this is a pneumatically shot concrete retainingwall, there is no need for level footings stepped vertically in 8″increments to accommodate for the block size used in the traditionalblock walls. The footing can simply be excavated to the specified depthbelow the lower finished grade (11) following the existing said gradeuniformly (5). This will save time and materials for the excavating,concrete, and other material costs. The plan view as shown in FIG. 6shows that as a retaining wall may change in vertical height (forinstance going from a 3 foot vertical height (7), to a 9 foot verticalheight (7)). The footing can make a smooth linear transition (27)instead of the stair stepping affect commonly used in traditional blockand concrete retaining walls (26). The vertical portion of thisretaining wall (7) can also be constructed with a batter or slope (SeeFIG. 7) (29). Because the backfilled soil or earth (12) exerts atriangular load on the vertical portion of the retaining wall (28),resulting in a zero load at the top and a large load at the bottom: abattered design is the most structurally effective and cost efficientmethod to construct his portion of the retaining wall. The traditionalblock walls must stair step the design (31). Again stair stepping is noneffective use of material and adds additional un-needed costs.

Monolithic Constructed Wall

This pneumatically applied concrete retaining wall can be constructed intwo concrete phases (the footing and vertical wall), much like in thetraditional block and concrete retaining wall construction methods.However, this pneumatically constructed retaining wall can also beconstructed monolithically by pneumatically by applying the concrete,for the footing and the vertical wall, in one step. This method wouldeliminate a cold joint or non-monolithic wall (FIG. 7) (30). Thisretaining wall would yield a higher strength when constructedmonolithically. A block wall by it nature cannot be built monolithically

Alternate Construction Methods

Because this retaining wall has no forms, more efficient cross sectionalshapes can be achieved in the design and construction. One such shape ofthe vertical wall cross section would be a “T” beam shape (FIG. 8). Inthis case, the backing board (13) would be attached to the opposite sideof the fill side (12). The rebar (8) would be the structural steeldesigned to withstand the tension exerted on the wall. The other rebarin the vertical wall (32) (9) is mainly needed to attach and stabilizethe backing board (13) attached with fasteners (14) While the shotcreteor pneumatic concrete is being applied. After the first phase ofconcrete has bee shot in (34), the second phase (33) can then be appliedor constructed. This “T” Beam affect will result in a more effective useof the concrete material. Since the backfill or soil load is negligibleat the top of the vertical retaining wall, a taper can be constructed atthe top (FIG. 9) (35). This would be used to create a more aestheticallyappealing wall at the top after the backfilling (12) has occurred.

Footing Key Construction

A key can also be constructed in the footing (FIG. 9) (36). This keywould, in some cases, allow the footing base (5) to be reduced in size.This key would help decrease the sliding factor of the overall retainingwall.

Extra Support and Bracing

As some of these walls increase in vertical height, the need foradditional bracing may be required (See FIG. 10). This temporary bracingcan be accomplished by installing temporary guy wires (38). The guywires can be attached to the vertical rebar (8) and the be stabilized bya stake (37) (pole, post rebar) secured in the ground as to stabilizethe guy wire (38) and the vertical rebar (8). This method is required inthe cases when the vertical rigidity is required to stabilize thebacking board and rebar when applying the pneumatic concrete. These guywires and simply be cut after the shotcrete or concrete has started tocure. The stakes can also be removed at that same time.

Alternate Footing Shapes or Construction

This method of retaining wall construction can accommodate orincorporate a variety of footing shapes and designs. For instance “L”shape footings, reverse footings (backfill on the opposite side),footings with a turn downs or key downs, or even areas where no footingsare required (for instance: bedrock or other existing solid materials).The footing, for this method of retaining wall construction, can also beconstructed with a traditional poured in place footing or any other typeor style of footing.

Alternate Vertical Wall Shapes

This method of retaining wall construction can have many alternate crosssectional shapes. For instance “T” shape, waffle shape, corrugated orany other structural or aesthetically pleasing.

Alternate Materials

This pneumatically applied concrete wall can have a substitution of anymaterial. For instance, the rebar as noted in this design can besubstituted with any material that yields a tensile strength (i.e.Carbon Fiber, graphite, metals, alloys, etc.). The Pneumatically appliedor sprayed on Concrete can also be substituted by using any materialwhich yields a high compressive strength (i.e. Mortar, gunnite, glues,epoxies, etc.).

Vertical Rebar Spacing

The design and construction of this retaining wall allows the verticalrebar to be sized and spaced where best suited structurally andeconomically. The spacing is not dependant on cell locations on Masonryor CMU (Concrete Masonry Unit) Blocks.

1. A method where forms are not required for the construction of aconcrete (or any high compressive strength material) retaining walls,consisting of an inner and outer vertical face comprising the followingsteps: excavating a footing, installing rebar for the footing and thevertical wall (horizontal and vertical), then attaching a backing boardor peg board to one side of the vertical wall rebar (leaving a minimumof a 2 inch gap). The concrete is then pneumatically applied against thepeg board until the desired wall thickness is achieved.
 2. The method ofclaim wherein not having two exterior forms as to enclose the inner andouter face of the vertical retaining wall. Said retaining wall comprisesthe further steps of: a. Excavating earth for the footing. b.Installation of all rebar for both the footing and the vertical wall. c.Attaching the peg board or backing board to one side of the verticalportion of the retaining wall. d. Pneumatically applying the concrete tothe footing and against the peg board as to construct the vertical wall.This method can be done in one step which allows the wall to beconstructed monolithically.
 3. The footings do not have to be verticallystair stepped in 8″ increments as traditional block, due to thepneumatically sprayed concrete being free formed and not being limitedto block size or shape.
 4. The footings do not need to be verticallylevel, again due to pneumatically sprayed concrete not being limited toblock size and laying block.
 5. The wall can be constructed utilizing amonolithic footing and vertical wall. Because this retaining wall doesnot have forms that will need to be removed, the wall footings andvertical portion of the retaining wall can be shot or constructedsimultaneously, pneumatically sprayed, in one step. This will in turnresult in a stronger wall than the traditional block retaining walls(cold joint between the footing and vertical retaining wall).
 6. Thefooting's shape on the horizontal or plan view section can betrapezoidal instead of stair stepping, again due to the limitation ofblock sizes. As the vertical height of the wall changes incrementally,the footing width can change along with the wall height maintaining atrapezoidal shape and thereby avoiding stair stepping the horizontalshape of the footing.
 7. The strength of the retaining wall can bechanged by simply altering the strength of concrete. 3,000 psi or 4,000psi concrete can easily be used which far surpasses the standardstrength of the standard concrete masonry unit (CMU) which is typically1,500 psi.
 8. As per claim 7, because the concrete strength can beincreased: a wall designed for 2,500 psi concrete can be constructedusing 4,000 psi concrete and thereby allowing the wall to be backfilledearlier than a traditional retaining wall when the curing strengthreaches said 2,500 psi.
 9. The vertical portion of the wall can avoidhaving a stair step effect. When standard block walls are constructedthe walls may stair step from 16″ to 12″ to 8″. Again this is due to thelimitations of the block sizes. The vertical portion of the retainingwall can be shot with a sloping or battered face or back. This moreaccurately models the standard triangular load, which the backfilledsoil, exerts on the vertical portion of retaining walls.
 10. Because ofthe lack of forms, the vertical portion of the retaining wall asmentioned in claim 9 can be designed and constructed by using a “T”shape or any other shape as to achieve a more structurally sound wall ormore aesthetically appealing wall.
 11. This wall because it ispneumatically applied can be constructed much quicker and with lesslabor or man hours required as that of the traditional retaining walls.This again is due to the fact that only one person is needed to applythe pneumatically sprayed concrete and one person to run the pump andtrowel or finish the outside face of the vertical wall.
 12. This wallcan be constructed in area that a block layer or mason may havedifficulty with the accessibility. This would also include hauling theblock and storing the block along with mixing or delivering the mortarand grout. The pneumatically sprayed concrete allows one man and aconcrete hose connected to a pump to access areas that would beotherwise be non-accessible places.
 13. Materials can be saved becausesoil loads are triangular there is no need for walls to be 8″ thick ontop. The load of the top of a retaining wall is 0 psi. Therefore thewall thickness at the top of the wall can be reduced to as little as 4″instead of the standard block wall of 8″.
 14. Site walls can beconstructed using this same method with the backing board being doubledup in the middle creating a hollow space in the center and therebysaving material.
 15. The vertical rebar spacing in the vertical wall asmentioned in claim 1, can be spaced at the location that is moststructurally and economically efficient. This rebar spacing will not bedependant on the location of the cells located within the block (i.e.every 8 inches)